Vacuum tube



A ril 12, 1960 w. G. SHEPHERD 2, 3

VACUUM TUBE Filed July 21, 1954 5 Sheets-Sheet 1 //6 ii I F/GJ F/6.2

IN V EN TOR. VV/LL/AM 6'. Jl/EPHERD ATTORNEYJ April 12, 1960 w. e.SHEPHERD 2,932,759

VACUUM TUBE Filed July 21, 1954 5 Sheets-Sheet 2 F76. ll

IN V EN TOR. VV/LL/AM GSHEPHERD W M L A'T-roR/vE Ys April 1960 w. G.SHEPHERD 2,932,759

VACUUM TUBE Filed July 21, 1954 5 Sheets-Sheet 3 IIIHIIIIIIIH IIIIIHHHIIINVENTOR. VV/LL/AM G. SHEPHERD ATToR/VEK;

A ril 12, 1960 w. G. SHEPHERD VACUUM TUBE 5 Sheets-Sheet 4 Filed July21, 1954 IN VEN TOR. G.J/1EPHE/?0 B p 1 ay l V/LLIAM ATTORNEYS April 12,19 w. G. SHEPHERD VACUUM TUBE Filed July 21,

5 Sheets-Sheet 5 INVEN TOR.

flTToR/vEYJ VV/L L MM 6. SHEPHERD United States Patent VACUUM TUBEWilliam G. Shepherd, St. Paul, Minn., assignor to Regents of theUniversity of Minnesota, Minneapolis, Minn., a corporation of MinnesotaApplication July 21, 1954, Serial No. 444,773 11 Claims. (Cl. 313-337)This invention relates to vacuum tubes for use in electronic circuitsand to improved vacuum tube construction and manufacture. Moreparticularly the invention relates to strong rugged vacuum tubes whichare resistant to shock and which are substantially free from internalvibration, and to methods of making such tubes.

Conventional vacuum tube structures now in use employ metallic heaterelements. These elements are made of wire, usually tungsten, wound intoconfigurations such as double helices or spirals or simply folded. Theformed wire is usually coated with an insulating material which is firedinto a hard coating. This heater element is inserted into a cathodesleeve, generally of nickel, which carries an electron emitting coatingupon its outer surface. The internal heater is heated by the passage ofcurrent and by radiation heats the electron emissive coating. Theradiation from the internal heater is determined by its thermalemissivity radiating area and by its temperature. Because the surfacearea of the heater is generally much smaller than the surface area ofthe surrounding cathode sleeve it is necessary to operate the heater attemperatures considerably in excess of the temperature of'the emittingsleeve. Any break in the heater wire results in total failure of thetube. Any break in the insulating coating of the heater wire may resultin partial shorting between individual turns of the wire or between thewire and the cathode sleeve. Because the heater is usually supported byrather long leads to a base stemand by the frictional forces between theheater and cathode sleeve it is usually subject to motion within thetube. Motion of individual elements Within a tube not only increasestheir susceptibility to damage and subsequent failure but also sets upharmonics due to vibration of the parts which influence the performanceof the vacuum tube.

, A closely related problem is that arising in the construction ofnon-microphonic vacuum tubes because of relative movement between thecathode and the control grid. Conventional grids presently in use areusually wound on two parallel rod supports. The grid wires are usuallywound spirally on a mandrel holding the support rods. grid, the spacingbetween grid and cathode being determined by the shape of themandrelupon which the grid is wound. The grid and cathode are supportedby being inserted into mica spacers at each end. Any deformation of thecathode or the grid results in deviations from the designcharacteristics of the tube. The nature of this arrangement of grid andcathode necessarily prevents any tension on the grid wires so that theymay vibrate individually. Moreover, the section of the cathode itself isnot structurallystrong, but may be deformed by mishandling. V

, The principal object of this invention is to provide a va'c'nnm tubehaving an improved ceramic heater, cathode and grid construction andmethods of making such tubes. ji" "'other object of this i ventionisto'provide improved I rug-gee vacuum tube construction whereby the tubeis A cathode is inserted coaxially within the 2,932,759 Patented Apr.12, 1960 resistant to shock and substantially free from internalvibration.

It is another object of this invention to provide a ceramic heatingelement and cathode for an electronic vacuum tube and a method of makingsuch an electrode structure.

Still another object of this invention is to provide a new frame gridconstruction and method of making same.

Other objects of the invention will become apparent as the descriptionproceeds.

To the accomplishment of the foregoing and related ends, this inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following description setting forth indetail certain illustrative embodiments of the invention, these beingindicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

The invention is illustrated by means of the drawings in which the samenumerals refer to corresponding parts and in which:

Figures 1, 2 and 3 are perspective elevations of the several componentsmaking up the heater element and cathode of this invention;

Figure 4 is a vertical sectional elevation of another embodiment of theheater element and cathode;

Figure 5 is a perspective elevation of one form of grid constructionaccording to this invention;

Figure 6A is a plan view of one form of construction of the grid;

Figure 6B is an end elevation of the grid material of Figure 6A;

Figure 7 is a plan view of another form of grid construction;

Figure 8 is a vertical section taken along line 8-8 and in the directionof the arrows of Figure 7;

Figure 9 is a top perspective view of tension means for one form ofgrid;

Figure 10 is a fragmentary perspective View of a ceramic heater andcathode set in place within the grid structure;

Figures 11 and 12 are alternative forms of grid and cathodeconstruction;

Figure 13 is a simplified assembly embodying a heater, cathode and agrid formed according to this invention;

Figure 14 is an exploded perspective view, partly broken away, of avacuum tube body;

Figure 15 is a perspective view, partly broken away, of a completevacuum tube constructed according to this invention;

Figure 16 is an enlarged vertical section through the tubeof Figure 15;

, Figure 17 is a transverse section through the vacuum tube taken alongthe line 1717 and in the direction of the arrows of Figure 15; and

Figure 18 is a similar section taken along the line 18-18 and in thedirection of the arrows of Figure 15.

Referring now to the drawings and particularly to Figures 1 to 4, thereis here shown in detail the construction of the ceramic heater andcathode structure. As shown in Figure l the structure comprises a heaterbody 10 having a central portion formed of a conductive ceramicmaterial, such as a high alumina body impregnated with metal. Forexample, the body may be the type designated AI 200 manufactured by theCoors Porcelain Company of Golden, Colorado. At least the lower end ofthe ceramic body is non-conducting. The ceramic heating element 10 maybe formed in sections and bonded together. For example, non-conductingceramic end sections may be bonded to a central metal impregnatedconducting section. Heater body 10 has a central aperture'll runningthroughout its length into which a metal conductor 12 may be fitted andbonded to the conductive portion of the ceramic body. Conductor 12 maybe a solid rod or may desirably be tubular and is provided with aconnecting lead-in wire 14.

The cathode structure includes a metal sleeve or areas of depositedmetal or metal plates 15 bonded to the central portion of the outersurfaces of the ceramic heater body, the plates carrying electronemitting coating on their outer surfaces. This metal may be nickel, forexample. The cathode structure. is supported in part by means ofinsulating ceramic spacer sleeve 16 at either 'end of the heatingportionof the cathode. Sleeves 16 serve also to locate and support the gridstructure. The heater body is preferably conductive only in the areabetween the supporting sleeves 16. This is accomplished by impregnatingonly that area of the body with metal. The outer surfaces of thenon-conductive portion of the ceramic body below the cathode plates arecoated with metal to make connection between the cathode and theexternal surface of a finished tube. A spider 18 formed of somespring-like metal provides lateral support for the upper end of thecathode body with flexibility for differential expansion. The top end ofthe body 10 fits into an aperture 19 in the spider. Edges 20 are adaptedto urge against the inside surfaces of the ceramic bulb of the vacuumtube.

The triangular form of construction shown in Figures l, 2 and 3 is justone of several which may be used. Alternatively a round rod-like ceramicbody 21 having a heating. conductor element 22 in aperture 24 may beused as shown in Figure 4. The electron emitting cathode 25 is here inthe form of a metal sleeve bonded to body 21 and having an electronemitting coating at its outer surface. The heater element 22 and sleeve25 are connected by means of conductors 26 and 27 to a current source,28. The cathode structure may be in planar form as shown in Figure 12.

In the cathode construction as illustrated. the heating current flowsradially outwardly through the ceramic body andthe joule heating raisesthe temperature of the body. It will be recognized that even though theceramic body may crack either in a plane perpendicular to the axisof thebody or in a plane passing through the axis no interruption in currentflow will result. Because of the greater area of the heating elementlower heater temperatures are required. The resistance of the .heater islarge so that high voltage-low current heat source can be ,used. Becausethe end sections of the heater can be :made non-conducting and since theceramic body has some thermal impedance it becomes possible to supportthe heater by the ceramic body itself, thereby providing a sturdystructure resistant to shock and mechanical vibration.

7 ,One form of control grid is shown in Figure 5. The grid is preferablymade in triangular form since this is the strongest grid section whichcan be readily adapted to 'a coaxial type of electron tube. This form ofconstruction permits tensioning of the grid wires and produces astructurally strong grid, in addition to providing some springor'resiliency in the frame so that the grid wires will be continuouslyunder tension. The grid 30 is formed of three frames or panels 31 joinedat their edges '32. The panels are formed of a thin strong electricallyconductive metal such as molybdenum. The grid is of a size to form atight sliding fit with sleeves 16. Each panel is provided with anopening or window 34 corresponding in size and shape with the electronemitting plate 15 on 'the ceramic heater element. Each panel is providedwith a corrugation 35 to give it added strength, and to tension the gridwires. The tensioned grid wires 36 are stretched across the openings 34of each panel. A lead-in conductor 37 is provided to make connectionwith an external contact. Grid wires 36 are preferably formed oftungsten similar metal.

One. method offorming the grid structure is shown in 2,932,759 a A VFigures 6A and 6B. Two metal sheets 38 and 39, each having windows oropenings 40 punched through their surfaces and having corrugations 41 atthe edges of the grid panels are laid face to face. The grid wire 42 isthen wrapped tightly around and around the pair of sheets across theopenings and are brazed to the corrugations or swaged into notches 44formed in the corrugations. Thereafter, the sheets are separated andformed into the desired grid structure.

Another and preferred'rnethod of forming the, grid is shown in Figures 7and 8. As shown here, a sheet 45, from which the structure of Figure 5is formed, has a plurality of openings or windows 34 punched with aswage cut leaving projecting edges 47 on one surface.

The sheet is also provided with corrugations 35 for the a purpose ofproviding some spring tension in the grid. The projecting edges areprovided with notches to receive the grid wires. Two of these sheets arelaid face to face with the swage cuts uppermost and the fine grid wire48 is wound tightly around and around the sheets in the notches andacross the openings 34. Thereafter the 'wires are swaged into thenotches and the sheets are separated and formed into grid structures.The edges of the grid panels are brazed or spot welded and the excess ofthe metal sheet may be cut away. The excess wire 49 may be removed ifdesired leaving only lateral grid wires :36 in place in either of theseforms of construction.

' Instead of forming the grid structure with rigid frames around theopenings it may be desirable to cut away the top and bottom portions ofthe frames. As shown in Figure 9 the grid then comprises the lateralgrid wires 50 held between strips 51 of sheet metal brazed or spotwelded together. The grid wires are held under positive tension by meansof a spring spider 52 formed in the general configuration of across-section of the grid (triangular as shown) and having a pluralityof spring arms '54 to urge outwardly against the metal strips 51 andhold the grid wires 50 under tension.

Figure 10 shows a fragment of the ceramic heater element located andpositioned within the grid structure held in position by means ofinsulating ceramic sleeve 16. In Figure 11' there is shown analternative form of cathode in which the gridlaterals are parallel tothe axis simultaneously making possible a true coaxial structure cathodebody is provided with a round ceramic sleeve 55 at both ends. The gridmay be formed by winding by either of the described methods or by anysimilar method.

'The top and bottom frame members are cut away and a grid section havinga width corresponding to the circumference of round insulating sleeves55 is cut, wrapped around the cathode base and sleeves 55 and crimpedinto grooves 56 in the sleeves. Alternatively, the grid can be formed bypressing two frame portions around opposite sides of the cathode base,welding the resulting projecting pair of wings, cutting away the excessmetal and crimping the grid structure into grooves 56. The expansion ofthe ceramic body during heating serves to tension the grid wires.

. A plane-parallel cathode structure is shown in Figure '12. Here, theceramic heater body 58 and the center conductor 59 of the heater arerectangular .in crosssection. The opposed surfaces of the body 58 eachhave acathode plate 60 bonded to the ceramic base. A nonconductingceramic sleeve 61 at each end of the ceramic body 58 positions-andsupports grid structure 62. It is apparent that a cathode structure ofsquare cross-section may similarlybe made. I

,A' simplified assembly embodying the grid structure and' cathodeheaterof this invention is shown inFigure 13. The grid and heater are asheretofore described. These structures are enclosed within a ceramicenvelope 64 brazed to a ceramic stem 65. An anode 66 is formed by ametal sheet bonded to the inside surface of the envelope or by metaldeposited on the inside of the envelope. A conductive coating 67 forms aconnection between plate 66 and brazed joint 68 which providesconnection outside the envelope. The lower end 69 of the ceramic heateris non-conducting with a conductive coating 17 on its outer surface. Thebrazed joint 70 be tween the ceramic stem 65 and the lower end of theceramic heater body provides connection to cathode plates 15. A metallictubulation 71 brazed into the top of the envelope is provided fordrawing a vacuum and sealing off the tube.

In Figure14 there is shown a ceramic envelope body specifically adaptedto receive a triangular cathode structure. The tube body comprises athick rugged triangular ceramic envelope 72 and a triangular ceramicstem or base 74. Stem 74 is provided with an opening 75' for the gridconductor 37 and a larger opening 76 for the non-conducting base of theceramic heater body. The envelope has a tubulation 77 brazed in its top.Plates 78 formed of metal sheet bonded to the inside surfaces of theenvelope have a narrow depending portion 79 which lead out between theenvelope and the base to make outside contact.

Figures 15, 16, 17 and 18 show views of a completed strong rugged vacuumtube constructed according to this invention. Metalized patch contact 81provides the electrical connection for the heater element and contact 32provides connection through brazing seal 83 conductive coating 17 withthe cathode. Contact 84 connects to the grid structure and side contacts85 provide outside connection for the plates 78. In Figure 18 there isshown in dotted lines the portions 87 and 88, formed by the folds of thesheet from which the grid structure is made, which may be cut off afterthe panel portions 31 of the grid structure have been welded or brazedtogether.

In the finished vacuum tube the cathode grid assembly becomes anintegral part of the ceramic envelope. This is accompilshed by theextension of the ceramic heater through and brazed to the stem. The tubeis strong and rugged. 'It is resistant to shock. But, even if theceramic heater element should become cracked, because it is conductivethroughout the heating area and the cathode is bonded to the heater, itwill continue to function. Because the internal structure of the tube issubstantially rigid there is substantially no relative motion betweenthe cathode and the control grid and virtually'no vibration of the gridwires. The grid construction of this invention, besides being strong,permits tensioning of the grid wires.

It is to be understood that the applicability of the grid structure ofthis invention is not limited to use with the ceramic heater. n thecontrary such control grids may be used in conjunction with cathodes andheaters of conventional design and construction.

As many apparently widely diiferent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsherein.

What I claim is:

1. An electrode structure for electronic vacuum tubes comprising aceramic heater element, said ceramic element being electricallyconductive throughout part of its length and non-conductive throughoutthe rest of its length, a conductive heating element within said ceramicelement, a metal cathode bonded to the outer surface of the ceramicelement adjacent the conductive portion thereof, conductor means forconnecting said heater element to a current source and a conductivecoating over the non-conductive portion of the ceramic element forconnecting the cathode to a current source.

2. An electrode structure for electronic vacuum tubes comprising aceramic heater element, said ceramic element being impregnated withmetal throughout part of its length to render it electricallyconductive, the remainder of said ceramic element being non-conductive,a conductive heating element within said ceramic element and bonded tothe conductive portion thereof, a wire conductor for connecting saidheating element to a current source, a metal cathode bonded to the outersurface of the ceramic element adjacent the conductive portions thereofand a conductive coating over the non-conductive portion of the ceramicelement for connecting the cathode to a current source. I

-3. An electrode structure for electronic vacuum tubes comprising anelectrically conductive ceramic heater element, a conductor within saidheater element, a metal cathode bonded to the outer surface of saidheater element and means for connecting said heater element and saidcathode to a source of electric current, insulating sleeves fitted onsaid ceramic heater element adjacent each end thereof and a control gridsupported on said insulating sleeves spaced apart from said cathode,said grid comprising a metal frame surrounding said ceramic element, anopening in the frame opposite the cathode and fine substantiallyparallel grid wires extending across said opening.

4. An electrode structure for electronic vacuum tubes comprising aceramic heater element, said ceramic element being electricallyconductive throughout part of its length and non-conductive throughoutthe rest of its length, a conductive heating element within said ceramicelement, a metal cathode bonded to the outer surface of the ceramicelement adjacent the conductive portion thereof, conductor means forconnecting said heater element to a current source and a conductivecoating over the non-conductive portion of the ceramic element forconnecting the cathode to a current source, insulating sleeves fitted onsaid ceramic heater element adjacent each end thereof and a control gridsupported on said insulating sleeves spaced apart from said cathode,said grid comprising a metal frame surrounding said ceramic element, anopening in the frame opposite the cathode and fine substantiallyparallel grid wires extending across said opening.

5. An electrode structure for electronic vacuum tubes comprising aceramic heater element, said ceramic element being impregnated withmetal throughout part of its length to render it electricallyconductive, the remainder of said ceramic element being non-conductive,a conductive heating element within said ceramic element and bonded tothe conductive portion thereof, a wire conductor for connecting saidheating element to a current source, a metal cathode bonded to the outersurface of the ceramic element adjacent the conductive portions thereofand a conductive coating over the non-conductive portion of the ceramicelement for connecting the cathode to a current source, insulatingsleeves fitted on said ceramic heater element adjacent each end thereofand a control grid supported on said insulating sleeves spaced apartfrom said cathode, said grid comprising a metal frame surrounding saidceramic element, an opening in the frame opposite the cathode and finesubstantially parallel grid wires extending across said opening.

6. An electrode structure according to claim 5 further characterized inthat the cross section of said ceramic heater element is triangular,each face surface of said ceramic element has a metal cathode bondedthereto and said control grid is triangular and coaxial with the ceramicelement having an opening in each of the three panels opposite from andspaced apart from said cathodes.

7. An electrode structure for electronic vacuum tubes comprising aheater element and cathode, conductor means for connecting the heaterelement and the cathode to current sources, an insulating sleeve fittedon at least one end of said heater element and a control grid supportedon said insulating sleeve spaced apart from said cathode-said gridcomprising a metal frame surrounding the heater element, an opening inthe frame opposite the cathode surface and hire substantially parallelgrid wires extending across said opening. a

8. An electronic vacuum tube comprising a ceramic base structure and aceramic envelope brazed thereto, said envelope enclosing an electrodestructure comprising an electrically conductive ceramic heater element,a conductor within said heater element, a metal cathode bonded to theouter surface of said heater element and conductor means from the heaterelement and cathode extending through the ceramic base for connectingsaid heater element and said cathode to a source of electric current,insulating sleeves fitted on said ceramic heater element adjacent eachend thereof and a control grid sup ported on said insulating sleevesspaced apart from said cathode, said grid comprising a metal framesurrounding said ceramic element, an opening in the frame opposite thecathode and fine substantially parallel grid wires extending across saidopening, one end of said ceramic heater extending through the ceramicbase and being brazed thereto, at least one plate bonded to the innersurface of said envelope and means connecting said plate to an externalcontact.

9. An electronic vacuum tube comprising a ceramic base structure and aceramic envelope brazed thereto, said envelope enclosing an electrodestructure comprising a ceramic heater element, said ceramic elementbeing electrically conductive throughout part of its length andnonconductive throughout the rest of its length, a conductive heatingelement within said ceramic element, a metal cathode bonded to the outersurface of the ceramic element adjacent the conductive portion thereof,conductor means from the heater element extending through the ceramicbase for connecting said heater element to a current source and aconductive coating over the non-conductive portion of the ceramicelement for connecting the cathode to a current source, insulatingsleeves fitted on said ceramic heater element adjacent each end thereofand a control gn'd supported on said insulating sleeves spaced apartfrom said cathode, said grid comprising a metal frame surrounding saidceramic element, an opening in the frame opposite the cathode and finesubstantially parallel grid wires extending across said opening, one endof said ceramic heater extending through the ceramic base and beingbrazed thereto, at least one plate bonded to the inner surface of saidenvelope and means connecting said plate to an external contact.

10. An electronic vacuum tube comprising a ceramic base structure and aceramic envelope brazed thereto, said envelope enclosing an electrodestructure comprising a ceramic heater element, said ceramic elementbeing impregnated with metal throughout part of its length to render itelectrically conductive, the remainder of said ceramic element beingnon-conductive, a conductive heating element within said ceramic elementand bonded -to the conductive portion thereof, a wire conductorextending from the heater element through the ceramic base forconnecting said heating element to a current source, a metal cathodebonded to the outer surface of the ceramic element adjacent theconductive portions thereof and a conductive coating over thenon-conductive portion of the ceramic element for connecting the cathodeto a current source, insulating sleeves fitted on said ceramic heaterelement adjacent each end thereof and a control grid supported on saidinsulating sleeves spaced apart from said cathode, said grid comprisinga metaLfra'me' sur rounding said ceramic element, .an opening in theframe opposite the cathode'and fine substantially parallel grid wiresextending across said opening, one end of said ceramic heater extendingthrough the ceramic base and being brazed thereto, at least oneplatebonded to the inner surface of said envelope and means connecting saidplate to an external contact.

11. An electronic vacuum tube according to claim 10 furthercharacterized in that the cross section of said ceramic heater elementis triangular, each face surface of said ceramic element has a metalcathode bonded thereto and said control grid is triangular and coaxialwith the ceramic element having an opening in each of the three panelsopposite from and spaced apart from said cathodes.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Kohl: Materials Technology for Electron Tubes, Reinhold Pub.Corp., New York, 1951, pages 347 and 399 (Reference 2).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,932,759 April 12, 1960 William G. Shepherd It is herebfi certifiedthat error appears in the-printed specification of the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

Column 8, line 3 1 list of references cited under "UNITED STATESPATENTS", for the patent number "l 70l 256" read 1,701,356

Signed and sealed this 13th day of September 1960 (SEAL) Attest: KARL H.AXLINE ROBERT c. WATSON Commissioner of Patents Attesting Officer

